And if it really is a critical industry, being dependant on available foreign labor is quite the risk. There's not really any guarantee they'll want to keep moving here.
Also, the US economy is already overly dependent on foreign labor. From offshoring jobs to manufacturing to onshore labor, every sector of the economy is filled with foreign labor. How many things you own were made outside of the US? How many of your coworkers are immigrants? How many foreigners do you interact with when working on a large project at work?
The only issue is if we underpay the immigrants. If Joe Schmoe American isn't the better pick then he shouldn't get the job over someone in a visa queue.